Conventional semiconductor devices are typically formed in a bulk substrate or a semiconductor material such as silicon, gallium arsenide, germanium, or the like. Recently, devices formed from film layers with mismatched atomic lattice structures have been used to engineer the properties of the film layer materials. This approach has been used to form semiconductor layers over an insulator to separate the active layer from the bulk of the semiconductor wafer. For example, silicon-on-insulator (SOI) semiconductor devices typically have a thin layer of silicon, also known as the active layer, on an insulator layer such as a buried oxide (BOX) layer. Active devices, such as MOS transistors (MOSFETs), are formed in active regions within the active layer and are isolated from the substrate by the BOX layer. In other examples, film layers such as oxides, nitrides, oxynitrides, carbides or the like may be formed over conductors, semiconductors, or insulators to provide structures with electrical insulation, physical barriers, fabrication masks, protective layers, or the like.
Devices formed on films on substrates exhibit many improved performance characteristics over their bulk substrate counterparts. SOI substrates, for example, are particularly useful in reducing problems relating to reverse body effects, device latch-up, soft-error rates, and junction capacitance. Such SOI technology therefore enables higher speed performance, higher packing density, and reduced power consumption. However, structures with film based elements are not limited to SOI structures, as any suitable material may be formed from a film over a structure such as a substrate, base, carrier, support, or other underlying structure.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.